1. Field of the Invention
This invention relates to a plasticizing assembly for use in an injection molding machine, which plasticizing assembly comprises a plasticizing cylinder comprising a nozzle section, a cylinder section, and clamping means holding said nozzle section and cylinder section together in axial alignment, also comprises heating means for plasticizing plastic material in said cylinder section, a feed screw, which is operable to rotate for feeding plastic material being plasticized in said cylinder section toward said nozzle section and to perform an axial stroke for injecting plasticized plastic material from said nozzle section, and a back flow valve for preventing a back flow of plastic material during said stroke,
which plasticizing assembly also comprises a carrier block, in which said cylinder section is mounted near its rear end.
wherein a skeleton is provided, which surrounds said cylinder section between said carrier block and the location of the foremost position of said back flow valve and comprises skeleton elements for protecting and supporting said plasticizing cylinder, inclusive of said heating means,
wherein said nozzle section is formed with a nozzle orifice for discharging said plasticized plastic material along a predetermined injection axis and with a needle-guiding bore, which communicates with said nozzle orifice and is inclined relative to said injection axis, and a valve needle for opening and closing said nozzle orifice is longitudinally slidably mounted in said bore,
wherein said plasticizing assembly comprises a valve-actuating cylinder, which is disposed adjacent to said carrier block and operable in a direction that is parallel to said injection axis to displace said valve needle in said bore to open and close said nozzle orifice, and a force-transmitting linkage, which operatively connects said valve-actuating cylinder to said valve needle and comprises a rear link, which is parallel to said injection axis and connected to said valve-actuating cylinder, a forward link, which is parallel to said bore and connected to said valve needle, and a motion-deflecting lever, which on spaced apart axes is pivoted to a supporting structure and to said links and is arranged to transform a longitudinal movement imparted to said rear link by said actuating cylinder to a longitudinal movement of said forward link and said valve needle in the direction of said bore.
2. Description of the Prior Art
In a plasticizing assembly of that kind which is known from U.S. Pat. No. 4,886,439 the plasticizing cylinder is surrounded by a skeleton, which extends axially along an intermediate length portion of the plasticizing cylinder.
The basic structure of that skeleton has specifically been disclosed in FIG. 5 of U.S. Pat. No. 4,863,362 and its description and that disclosure is incorporated herein by reference.
In plasticizing assemblies of the kind described first hereinbefore the plasticizing cylinder is detachably mounted in a bore of the carrying block and the valve-actuating cylinder is disposed adjacent to the carrier block and adapted to be uncoupled from the force-transmitting linkage so that the valveactuating cylinder may be left in the injecting unit when the plasticizing cylinder is to be replaced. The motion-deflecting lever is pivoted to the nozzle section or to the cylinder section so that the motion-deflecting lever and its pivots will be subjected to extremely high temperatures during the injection molding operation and said lever and pivots must be made of heat-resisting castings having finished surfaces. Because the valve needle is rather short, the motion-deflecting lever and its pivots must be made with small manufacturing tolerances. For this reason the pivoting of the lever to the nozzle section or cylinder section involves relatively high manufacturing costs, particularly as regards the provision of pivot bearings for mounting the pivots of the motion-deflecting lever in the nozzle section or cylinder section.
In the known plasticizing cylinder the inclination of the needle-guiding bore relative to the injection axis is rather large, for various reasons, and amounts to about 30.degree.. As a result, the intersection between the inclined bore and the axially extending nozzle orifice is relatively short so that the closing of the nozzle orifice will be facilitated. Besides, a large inclination is required in view of the adjacent clamping ring, the forward end of the cylinder section and the adjacent heating element. These adjacent parts would render the mounting of the valve needle in a bore haivng a smaller angle of inclination extremely difficult.